1. Field of the Invention
This invention relates to a manhole closure assembly, and more specifically, to a manhole closure assembly including a unique valve assembly for relieving pressure inside a manhole, and a unique locking assembly for locking a removable cover plate of the manhole assembly in sealing relationship with a manhole opening.
2. Description of the Prior Art
It is highly desirable to employ manhole closure assemblies for sealing a manhole opening associated with a sewage treatment plant to segregate drainage and storm water from the plant. Otherwise, the sewage treatment facility would be subjected to the unnecessary burden of having to cope with the excess fluids provided by drainage and storm water. Representative prior art manhole assemblies are disclosed in U.S. Pat. No. 3,621,623, issued to Downes and U.S. Pat. Nos. 3,712,009 and 3,798,848, both of which are issued to Campagna.
Prior art manhole closure assemblies have included a pressure relief valve for relieving pressure inside of a manhole when the pressure therein exceeds a predetermined amount, as exemplified in the above-referred-to Campagna patents. The valve assemblies employed in the Campagna manhole closure assemblies are self-contained units which are installed within a removable cover plate. Specifically, the valve assemblies employ a separate body member which is fastened to the cover plate and a movable valve element extending through a valve opening in the body member. The valve element is normally biased to seal the valve opening, and is actuatable by the build-up of internal pressure within the manhole to unseal said opening.
Manhole closure assemblies with completely self-contained valve members of the type discloses in the Campagna patents are somewhat difficult to construct. Specifically, the closure plate of the assembly must be modified to receive the valve body through it, and care must be taken to rigidly secure the valve body to said cover plate.
The prior art manhole closure assemblies have not included reliable locking means for locking a removable cover plate in sealing relationship with a manhole opening in a substantially tamper-proof manner to minimize the possibility of a child removing the cover plate at an unattended site, and possibly becoming injured, or even killed, by falling into the manhole.